Supplement to Model-aided Design and Integration of Functionalized Hybrid Nanomaterials for EnhancedBioremediation of PFASs Using Supercritical Fluid Chromatography/Mass Spectrometry

文摘

ABSTRACT Global public health concern is growing over per- and polyfluoroalkyl substances (PFASs) toxicity, environmental persistence, and potential to bioaccumulate in humans and wildlife. Nearly every person who has been tested for PFASs shows measurable levels in their blood resulting from contamination of the environment and continued use in consumer products and industrial applications. In particular, drinking water appears to be the major source of PFAS exposure for people living near contaminated sites. Importantly, some PFASs have been linked to liver damage, developmental impacts, and several cancers (e.g., kidney, testicular). Environmental remediation is urgently needed, but efforts are hampered by the extreme persistence of the carbon-fluorine bond. Biodegradation typically involves only the non-fluorinated components of polyfluorinated PFASs, resulting in the creation of shorter-chain perfluorinated acids that are more persistent and mobile. Complete mineralization has not been demonstrated. Abiotic treatment technologies can be more effective but require extremely high energy inputs, and the degradation mechanisms are poorly understood. There is a critical need for a treatment technology with lower energy requirements, and for enhanced degradation pathways that efficiently mineralize PFASs without formation of perfluorinated acids that persist after treatment. The overarching goal of this proposal is to develop an innovative nanomaterial-biological strategy to tackle the challenge of PFAS biodegradation. Our central hypothesis is that pretreatment by tailored nanomaterials can facilitate transformation of structurally diverse PFASs to achieve more efficient and complete biodegradation. Our previous work has shown that functionalized nanohybrid catalysts incorporating reduced graphene oxide (rGO) and nano zerovalent iron (nZVI) can successfully initiate degradation of long-chain PFASs. Here, we will employ this abiotic transformation as an innovative pretreatment to unlock the biodegradation of PFASs. Leveraging our expertise in molecular modeling and ‘omics’ techniques, we will test and tailor the ability of microbial communities to more efficiently degrade pretreated PFASs and their initial degradation products. All degradation products will be characterized by high-resolution mass spectrometry and 19F-nuclear magnetic resonance spectroscopy to reveal the mechanisms that enable this nano-bioremediation strategy. This research will tackle a pressing environmental contamination problem with three complementary specific aims: Aim 1: Synthesize multifunctional redox-active nanohybrid materials and evaluate their catalytic properties for PFAS degradation (dehalogenation, degradation of long-chains to short-chains). We will synthesize and characterize two multifunctional and hierarchical carbon-metal nanohybrids: (i) redox-active reduced graphene oxide nano zerovalent iron (rGO–nZVI) and (ii) photocatalytic rGO-nZVI- titanium dioxide (TiO2) or rGO-nZVI-TiO2, and test the efficacy and extent to which they can transform and/or degrade PFASs under UV irradiation and/or H2O2 exposure. We will identify the PFAS degradation products and elucidate the associated chemical degradation pathways, kinetics, and mechanisms. Aim 2: Assess the efficacy of biodegradation and complete mineralization of PFASs and degradation products by enriched microbial cultures. Mixed anaerobic microbial communities that include known dehalogenators will be cultured with a range of short- and long-chain untreated and nanomaterial-treated PFASs to measure the removal efficacy and mineralization of PFASs. Microbial community structure and activity will be measured by 16s rRNA gene abundance and transcription levels of known reductive dehalogenases genes. Metagenomics and transcriptomics will be applied to elucidate microbial genomes and reductive defluorination pathways that are involved in PFASs biodegradation. Aim 3: Perform molecular modeling to discover, detect, and refine enzymatic biodegradation for structurally diverse PFASs. In silico tools, including molecular docking and molecular dynamics, have shown powerful potential for identifying PFAS-biomolecule interactions that can inform our understanding of PFAS toxicokinetics and toxicodynamics. Here, molecular modeling approaches will be used to identify strong interactions between structurally diverse PFASs and enzymes that have shown potential for degradation of persistent halogenated substances. The specific interactions between PFASs and amino acid residues in these enzymes will be identified; strategies, including community composition and directed enzyme evolution, will be investigated to allow tuning of molecular interactions to improve degradability of PFASs. Expected Outcomes: Our integrative approach has significant potential to advance our understanding of PFAS redox transformation mechanisms and biodegradation pathways. By combining our expertise in nanomaterial design, microbiology, chemical characterization, and molecular modeling, we will enable the design of a synergistic system to completely degrade, defluorinate, and mineralize diverse PFASs. This novel nano- bioremediation approach has the potential for inclusion and application within the treatment train for both PFASs- contaminated groundwater and drinking water sources. Knowledge on the PFASs degradation mechanisms at the molecular level will substantially advance the environmental remediation of this ubiquitous class of contaminants, and prevent further human exposure to these bioaccumulative and hazardous chemicals.